1. Field of the Invention
The present invention concerns electrically conductive oxides of the pyrochlore family based on copper and/or silver, lead, bismuth, and ruthenium, and electrically resistant materials that contain such oxides.
2. Description of the Related Art
A number of polynary oxides that contain ruthenium and bismuth, that have a pyrochlore crystalline structure, and that are appropriate because of their electrical properties as constituents of electrically resistant materials are known.
German Patent 1 816 105, for example, describes the electrically conductive stable bismuth ruthenate Bi.sub.2 Ru.sub.2 O.sub.7 with a pyrochlore-crystal structure and similar oxides of the pyrochlore or pyrochlore-related structure that contain other metals in addition to bismuth and ruthenium. They are employed in conjunction with glass to manufacture resistors. The specific resistance of resistors manufactured with Bi.sub.2 Ru.sub.2 O.sub.7 can be varied over a wide range maintaining a low temperature coefficient in the range of +25.degree. to +125.degree. C.
Electrically resistant materials that contain electrically conductive polynary oxides with a crystalline structure related to pyrochlore and of the general formula M.sub.x M'.sub.2-x M".sub.2 O.sub.7-z wherein M is silver and/or copper, M' is bismuth or a mixture of at least 1/2 bismuth and up to 1/2 cadmium, lead, yttrium, thallium, indium and/or rare earth metal and M" is ruthenium, iridium and/or a mixture of at least 3/4 ruthenium and/or iridium and up to 1/4 platinum and/or titanium and/or rhodium are described in German AS 2 403 667. The oxides are obtained by jointly heating the requisite oxides or readily oxidizing metals or salts to approximately 600.degree. to 1200.degree. C. subject to oxidizing conditions. At a proportion of 5 to 90% they constitute in conjunction with a glass frit or other appropriate inorganic binder the solid constituent of the resistant material, which also has a liquid organic carrier, a solution of ethyl cellulose in terpineol, for example, to render it susceptible to printing. Resistors with especially low specific resistances and a flat temperature response thereof can be obtained by firing the resistant material onto a dielectric substrate, aluminum oxide, for example, at approximately 650.degree. to 950.degree. C.
European Patent 110 167 concerns a method of manufacturing pyrochlore compounds of the general formula Bi.sub.2-x M.sub.x B.sub.2 O.sub.7-z, wherein M=cadmium, copper, lead, indium, gadolinium, and/or silver and B=ruthenium and/or iridium. These compounds have an extensive specific surface and are appropriate for resistors with relatively low temperature coefficients of resistance in the range of +25.degree. to +125.degree. C. (Hot Temperature Coefficient of Resistance: HTCR). They can be manufactured by annealing a mixture of the bismuth-oxide carbonate Bi.sub.2 O.sub.2 CO.sub.3, the dioxide of the ruthenium and/or iridium, and the carbonates of the other metals in an oxidizing atmosphere and purification the reaction product with a diluted aqueous mineral acid.